This proposal is directed at determining the role of the paternally expressed gene, PEG3, in ovarian cancer, and defining other imprinted genes at human 19q13.4 potentially involved in carcinogenesis. Preliminary data indicate that PEG3 is dramatically downregulated, and that the PEG3 promoter CpG island is hypermethylated in ovarian tumors. Bisulfite sequencing of DNA from ovarian tumors will be used to determine the frequency of PEG3 promoter region hypermethylation. There are at least three alternatively spliced PEG3 isoforms that are maternally imprinted and paternally expressed in a tissue-dependent manner. Two of these isoforms encode distinct zinc finger proteins that share upstream exons independent of the zinc finger domains. The third isoform is predicted to encode a truncated protein that is expressed in tissues together with the other PEG3 isoforms with the notable exception of heart and placenta, suggesting an important tissue-specific function. Transient transfection assays using PEG3-deficient ovarian cancer cell lines will be used to determine the influence of the three isoforms on cellular growth and apoptosis, both functions previously ascribed to mouse Peg3. These studies will help clarify the role of the human PEG3 isoforms in the control of cellular growth, and may further contribute potential diagnostic and therapeutic targets for ovarian cancer.